This invention relates to a raw materials charging device suitable for use in the field of steel making performed by using an electric furnace for preheating raw materials, such as scrap, by preheating.
Heretofore, in one process known in the art for preheating raw materials for steel making in a preheating furnace, the raw materials or scrap is introduced into the preheating furnace through its throat and released therefrom through its bottom. In another process known in the art, the direction of flow of the exhaust gas is reversed and it is introduced into the preheating furnace through its bottom and released through its throat. These processes of the prior art have suffered the disadvantage that only those raw materials which are disposed in the vicinity of a furnace wall are preheated and those raw materials which are disposed in a central portion of the furnace are difficult to preheat due to the exhaust gas blowing through between the furnace wall and the raw materials, with a result that difficulties are experienced in effecting uniform preheating of the raw materials in the furnace and full realization of the advantages from performing preheating is hampered.
To obviate this disadvantage, proposals have been made to form a passage through a stack of raw materials in the preheating furnace for gas of high temperature to flow therethrough to enable heat exchange to take place between the gas of high temperature and scrap of low temperature. This process is intended to reduce a pressure loss of the gas of high temperature blown through the furnace while enabling uniform preheating of the scrap to be performed. One example of a device suitable for carrying this process into practice is disclosed in Japanese Utility Model Publication No. 37039/82, which is constructed such that gas of high temperature is introduced through an upper portion of a bucket and released through a lower portion thereof. A main body of a jig is set in position in an empty bucket and raw materials for steel making, such as scrap, are charged into the bucket. Then, a suspended frame is moved upwardly to withdraw the main body of the jig from the bucket and form a plurality of gas passages in a stack of scrap. The bucket is conveyed to where a preheating pit is located to introduce waste gas into the bucket, which is then sealed by placing a hood thereon. The waste gas thus introduced into the bucket vigorously flows through the gas passages into layers of the scrap, and a pressure loss of the waste gas is reduced to one-half of its value in the prior art. Thus, the rate of heat exchange taking place between the waste gas flowing through the bucket and the raw materials for steel making charged into the bucket is doubled, thereby improving a heat recovery rate and increasing the speed at which the raw materials for steel making in the bucket are preheated. In this construction, the gas essentially flows only through the gas passages formed beforehand in the stack of raw materials before being released from the furnace, so that the device is considerably low in preheating efficiency. Also, since the exhaust gas is released through the bottom of the furnace, it is necessary to provide a bucket opening and closing mechanism with means for insulating heat when the exhaust gas used is high in temperature. This would cause a rise in production cost, and the device would have the additional disadvantage of being short in service life due to wear and deformation that might be caused thereon.